The purpose of this study is to determine whether age affects the transport of food through the stomach as well as the small intestine. Non-invasive techniques will be used to study GI function in elderly subjects. The specific aims are to establish normal values for gastric emptying, small bowel transit and colonic transit in healthy elderly subjects, to examine these values for effects of age, gender and body mass index, independent of disease, and to obtain comparable transit data from elderly subjects with functional bowel disease (chronic constipation), as identified by the investigator's population-based survey.